drm/rockchip: fix wrong pitch/size using on gem

args->pitch and args->size may not be set by userspace, sometimes
userspace only malloc args and not memset args to zero, then
args->pitch and args->size is random, it is very danger to use
pitch/size on gem.

pitch's type is u32, and min_pitch's type is int, example,
pitch is 0xffffffff, then pitch < min_pitch return true, then gem will
alloc very very big bufffer, it would eat all the memory and cause kernel
crash.

Stop using pitch/size from args, calc them from other args.
Signed-off-by: Mark Yao <mark.yao@rock-chips.com>

drivers/gpu/drm/rockchip/rockchip_drm_gem.c

@@ -234,13 +234,8 @@ int rockchip_gem_dumb_create(struct drm_file *file_priv,
 	/*
 	 * align to 64 bytes since Mali requires it.
 	 */
-	min_pitch = ALIGN(min_pitch, 64);
-
-	if (args->pitch < min_pitch)
-		args->pitch = min_pitch;
-
-	if (args->size < args->pitch * args->height)
-		args->size = args->pitch * args->height;
+	args->pitch = ALIGN(min_pitch, 64);
+	args->size = args->pitch * args->height;
 
 	rk_obj = rockchip_gem_create_with_handle(file_priv, dev, args->size,
 						 &args->handle);